Figure 38-20 CT scans showing severe pancreatitis evolving into pseudocysts (arrows) over 2 months. (Courtesy Dr. PerryPernicano.)
UC and Crohn's disease is 1.5 to 8 new cases per 100,000 U.S. population per year, more often in Caucasians and with no specific gender predominance, although some suggest a male predominance in Crohn's disease and a female predominance in UC. Most patients are diagnosed with IBD between ages 15 and 25, with a second peak between 55 and 65 years. The incidence of microscopic colitis is most likely underestimated because it is not well known; estimated incidence ranges from 4.3 to 9.2 per 100,000 in Western European and Icelandic population studies (Loftus, 2003).
Genetic factors play an important role in the development of IBD. First-degree relatives of patients with either form of IBD have been shown to have an almost 10% lifetime risk of developing disease and often present with a similar disease type and course as the affected family member (Higgins and Zimmerman, 2004).
Ulcerative colitis involves the mucosal layer of the sigmoid colon and rectum in the vast majority of cases, causing proctitis and proctosigmoiditis (Fig. 38-22). When there is proximal spread, it tends to be continuous and symmetric, causing intestinal mucosal inflammation with edema and friability that is visualized from the rectum proximally. Pan-colitis is caused by inflammatory exudates producing a backwash ileitis by way of a patent ileocecal valve, and can cause small bowel involvement.
Crohn's disease differs from UC in that it may involve any part of the GI tract from the mouth to the anus, including the gallbladder and biliary tree, and involves the entire thickness of the bowel wall. It is most often found in the immunologically rich terminal ileum, and Crohn's disease involves the rectum in less than 50% of cases. In contrast to UC, the mucosal abnormalities are discontinuous ("skip lesions"), asymmetric, and patchy, which account for obstruction, abscesses, and perianal fistulas and those to other organs and skin. Recurrent disease flares and healing can result in significant muscular hypertrophy and fibro-sis of the intestinal wall, leading to small bowel strictures, upstream dilation of intestine and increased fistula formation, and eventual bowel obstruction and the imminent need for surgical intervention (Higgins and Zimmerman, 2004).
Most patients with UC present with mild to moderate diarrhea without constitutional symptoms. Typically, the more severe the illness, the greater is the number of bowel movements, and the more likely that constitutional symptoms such as fever, fatigue, dehydration, and weight loss will also occur. UC can be intermittent with flare-ups, and remission can occur without therapy. A minority of patients with UC present with severe or fulminant panniculitis, ranging from an acute abdomen to toxic megacolon. Frequent urgent and bloody diarrhea usually suggests rectal disease and is most consistent with UC.
In patients with mild Crohn's disease, abdominal pain may be vague, the diarrhea intermittent, and weight loss absent. Postprandial crampy pain can suggest transient small bowel obstruction from inflamed or fibrotic, narrowed small bowel segments. Colonic involvement with Crohn's disease may present similar to UC, with predominantly bloody diarrhea. Rectal involvement produces more urgent and frequent small, bloody stools as a result of an inflamed, nondistensi-ble rectum. Mucus in the stool is nonspecific and is found in both IBD and irritable bowel syndrome (IBS) (Higgins and Zimmerman, 2004).
Extraintestinal manifestations may be the presenting symptoms of UC or Crohn's disease. Uveitis, iritis, or episcleritis often flare concomitantly with intestinal symptoms. Large-joint pain and sacroiliitis may be a form of entero-pathic arthritis. Common skin manifestations include erythema nodosum, perianal fistulas, and pyoderma gangrenosum. IBS is much more prevalent than IBD, and thus a major pitfall in the diagnosis of IBD is the mislabeling of patients with IBS.
The finding of confluent erythematous rectal inflammation is most consistent with UC and infectious colitis. Pseudopolyp formations indicate chronic inflammatory colitis (Fig. 38-23), while solitary aphthous ulcers, "rakelike" lesions, strictures, and rectal sparing are consistent with Crohn's disease. Colonoscopic evaluation should include ileal intubation and biopsies of both normal and abnormal mucosa. Anal or perianal lesions, including sinus tracts, rec-tovaginal fistulas, and abscesses, is consistent with Crohn's disease but not with UC. The mucosa in a patient with Crohn's disease may appear cobblestoned or nodular. Loss of haustra, distortion of normal architecture, or both may be found (Figs. 38-24 and 38-25).
Pharmacologic treatment of IBD is aimed at inducing remission and maintaining a symptom-free life, often after consultation with a gastroenterologist. Treatment of active flares with systemic steroids has been the mainstay of remission induction therapy, producing remission rates up to 70% in Crohn's disease versus 30% with placebo; similar results have been shown in the remission of UC. Budesonide, a nonsystemic steroid used in an enema formulation, has been effective for induction of remission in Crohn's disease and distal UC flares. Mild flares of UC are usually treated with 5-aminosalicylic acid (5-ASA) derivatives such as sulfasalazine, although RCTs have shown 5-ASA only marginally superior to placebo at controlling flare-ups of Crohn's disease. 5-ASA products are thought to be inferior to budesonide and systemic steroids for remission induction in Crohn's disease and generally are not used (Higgins and Zimmerman, 2004).
Azathioprine and its metabolite, 6-mercaptopurine, are slow-acting compounds proved effective for inducing ik
remission in Crohn's disease. They often are added to systemic steroids to help induce and maintain remission and to ease steroid tapering. Methotrexate is also effective for remission induction in Crohn's disease. Close monitoring of CBC and serum transaminases is recommended, with monthly testing on initiation and with dosage changes. Pregnancy and exposure to live-virus vaccines should be avoided. Infliximab, an anti-tumor necrosis factor alpha antibody, is remarkably effective in treating approximately 60% of steroid-resistant patients with Crohn's disease. Infliximab has significant side effect risks, including infusion reactions, and rarely, worsening of heart failure, activation of latent tuberculosis, serum sickness, and invasive fungal infections (Feagan, 2003).
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